Retrievable gas lift valve assembly



Dec. 24, 1968 DOUGLAS ET AL 3,417,774

RETRIEVABLE GAS LIFT VALVE ASSEMBLY Filed June 13. 1966 2 Sheets- Sheet1 Bobby -L. Douglas Stephen M. Foriadq s BY M ATTORNEY Dec. 24, 1968Filed June 13, 1966 B. L. DOUGLAS E A 3,417,774

RETRIEVABLE GAS LIFT VALVE ASSEMBLY 2 Sheets-Sheet 2 fig o Bobby L.Douglas- Stephen M. Foh'ades INVENTORS ATTORNEY United States Patent3,417,774 RETRIEVABLE GAS LIFT VALVE ASSEMBLY Bobby L. Douglas, Dallas,Term, and Stephen M. Fotiades, Harvey, La., assignors to DresserIndustries, Inc., Dallas, Tern, a corporation of Delaware Filed June 13,1966, Ser. No. 557,081 8 Claims. (Cl. 137-155) This invention isconcerned with a gas lift flow valve used in production of oil and gasfrom wells and is particularly concerned with a wireline retrievableflow valve of the pressure charged type with integral check valve whichmay be used in conventional offset mandrels now in use in the field.

It is the primary object of the invention to provide a pressure chargedvalve assembly in which the natural relationships between operatingpressure, pressure dome volume, bellows size, bellows stroke, valvesize, and operating tubing pressure may all be used for maximumoperating characteristics and efiiciency.

A problem has been caused in the gas lift industry by a universally usedstandard side-pocket or offset mandrel for wireline retrievable gas liftflow valves. The spacing of the sealing elements on the valve housingfor functional engagement between the valve and the mandrel is fixed,and the length of the flow valves is determined by the necessaryclearances for attachment of running and retrieving tools. Furthermore,the latch mechanism by which the flow valve is seated and retained inthe mandrel is fixed by certain dimensional limitations.

In the present invention, there has been provided a valve with anenlarged pressure dome which is functionally equivalent to a much longervalve or one of much greater diameter than would be required in theabsence of the above limitations, yet which will fit into andfunctionally operate in the offset mandrel now in the field.

The most important physical characteristics of a pressure operated flowvalve for efiicient use are: the volume of the pressure dome (excludingthe volume which may or may not be filled with a non-compressible fluidfor safety purposes), the effective area of the bellows, the stroke ofthe bellows necessary to obtain full opening of the valve element, andthe area of the port through which fluid flow is controlled by the flowvalve. A functional characteristic which is highly important is the useof an adequate check valve which will control back-flow of fluidsthrough the valve under high pressure acidizing, treating, orhydrostatic pressure conditions and yet allow the true operating tubingpressure of the installation to be effective during the operating cycleon the area of the valve element equal to the area of the port throughwhich the gas injected.

The above characteristics determine the four critical pressures requiredfor efiicient use of gas lift in secondary recovery. These four criticalpressures are (1) the pressue of the compessible fluid in the pressuredome, (2) the maximum operating pressure desired, (3) the openingpressure of the flow valve (pressure required to crack the valve), and(4) the tubing pressure present and effective against the valve elementover the area equal to the valve port at the time the valve is cracked.

The opening pressure of the valve is determined by an equilibrium pointat which time the dome pressure acting across the effective area of thebellows equals the sum of the casing pressure (actually the openingpressure), plus the tubing pressure acting across the area of the port.

This equilibrium point is also affected by the spring tension in thebellows, which is usually negligible but which can be easily correctedfor. It should be obvious that when the flow valve is cracked, theinjection gas,

being opposed by inertial load due to the liquid slug is Patented Dec.24, 1968 to be recovered from the well, rapidly approaches and becomessubstantially equal to the casing pressure at the opening point.

The valve stroke is a design characteristic of the flow valve. It shoulddefinitely be long enough to completely open the valve port forinjection of gas and yet should not be longer than this "because of theinduced fiexure of the bellows, which will rapidly use up the fatiguelife thereof and cause ultimate-failure of the valve.

The volume of the pressure dome is also a design feature of the flowvalve inasmuch as the increase in pressure therein due to the stroke ofthe valve and its compressive action on the gas in the dome results in amaximum dome pressure which should be smaller than the opening pressureof the valve. That is to say, the maximum pressure in the pressure domewhen the valve is full open should be less than the opening pressure ofthe valve.

The reason for the foregoing conclusion is as follows: from an ideal andefliciency standpoint, the opening pressure of the valve and the closingpressure of the valve should represent a pressure drop over the annulusvolume containing the gas to be injected sufiicient to lift thepredetermined slug of liquid from the hole. Highest efficiency from theinstallation will be obtained when this condition is most nearlypresent. The stroke of the valve is and should be designed into thevalve with certain mechanical limitations. However, if inadequate volumeis designed into the pressure dome, the maximum dome pressure willresult before the full stroke of the valve has been obtained andinefiicient injection will follow resulting from premature reversestroke of the valve toward the closed position, causing throttling whichfurther decreases efficiency. If the designed pressure dome volume issuch that the maximum pressure in the dome results concurrently with themaximum stroke of the valve, full opening will be instantaneouslyachieved, but the premature reverse stroke of the valve toward closedposition will immediately result from a drop in pressure in the annulusbefore the valve has remained open for the desired time and throttlingwill result with loss of efficiency.

Therefore, a dome volume should be provided which will result in a fullstroke of the valve but having a maximum dome pressure considerably lessthan the opening pressure of the valve so that the valve will be allowedto remain full open through a substantial and calculable portion of therange of the annulus pressure drop.

The above comments apply to intermittent gas lift flow wherein fullvalve opening is. required. However, in continuous gas lift flow, theoperating pressure range of the valve is ideally in the throttling rangeand it should be obvious that the limitations of the pressure domevolume should be such that it can [be designed for the ideal situationin either intermittent or continuous flow. This has been an ever presentproblem in the gas lift industry, the solution to which has beenapproached in valves not restricted in their design parameters by theuniversally used side-pocket mandrels as mentioned above.

Now, this present invention allows a solution of this problem even underthe restricted parameters described in connection with valves used inside pocket mandrels.

Of further importance in the design of an efficient gas lift valve andgas lift installation is the check valve assembly. The check valve mustetficiently control back flow through the flow valve under conditions ofacidizing, tracing, treating, etc.; and in the absence of any otherproblems, a straight spring-loaded check valve would be suitable.However, since the tubing pressure effective over the area of the porton the valve ball of the flow valve is a vital factor in the design ofthe flow valve, especially as port sizes increase for more rapid andefficient injection of gas, and since the nature of gas lift assumesthat the closing pressure effective against the port area of the flowvalve will be somewhat lower than the opening pressure effective againstthe port area due to the fill in of fluid to be ejected, a spring-loadedcheck valve usually prohibits the true reflection of the tubing pressureon the valve stem and thereby prohibits the effective use of the tubingpressure in design calculations for flow valves or installations.

A straight velocity check valve would be effective in allowing the truetubing pressure to be reflected on the valve stem, but is highlyineflicient in controlling the backflow under the many conditions ofvelocity to which said backflow is subjected.

In the present invention, there is disclosed a check valve which isspring loaded to a position of restricted flow which will allow the truetubing pressure to be reflected on the valve stem under conditions ofno-flow, but will immediately react and be highly effective incontrolling backflow under treating conditions.

A suitable embodiment of the invention is shown in the attached drawing,wherein,

FIGURES 1 and 1A are a quarter-section elevational view of a preferredembodiment of the gas lift valve herein described showing it mounted ina conventional side pocket mandrel.

Numeral references are employed to designate the various parts shown inthe drawing.

DESCRIPTION Referring to FIGURE 1, there is a latch nose 1, which has anupwardly and inwardly tapered contour 2 thereon which is functionallyadapted to facilitate attachment of the flow valve to a running tool andto guide a retrieving tool onto and about the flow valve. There is adownwardly facing shoulder 3 and an undercut section 4. The undercutsection and the downwardly facing shoulder 3 are adapted to hold theflow valve in the running tool. A suitable form of running tool isdescribed under the title KB-2 running tool on p. 111 of the 1964-65Edition of the Composite Catalog of Oil Field Equipment and Services.

The mating threads 5 rigidly attach the latch nose 1 to a pressure dome6 having a portion 7 about which a latch sleeve 8 is arranged. Thecompanion threads 9 connect a latch seal retainer 10 to pressure dome6-. The latch seal retainer 10 has an upwardly extending portion 11 andan upwardly facing shoulder 12. The upwardly extending portion 11 isarranged for slidable engagement with the latch sleeve 8 and theupwardly facing shoulder 12 is arranged to limit the downward movementof a downwardly extending enlarged portion 13 of the latch sleeve 8. Alatch dog 14 is slidably arranged about portion 13 and is seated on theupwardly facing shoulder 12. There is an undercut portion 15 in theouter surface of the latch sleeve 8 and a downwardly facing shoulder 16is formed thereabout.

The latch spring 17 abuts the downwardly facing shoulder 16 of the latchsleeve 8 at the upper end and abutts the upper surface 18 of the latchdog 14 at the lower end thereof. There is an upwardly facing taperedshoulder 19 on the latch sleeve 8. The latch sleeve 8 is disengagedlyattached to the pressure dome 6 by means of shear screws 20. There isalso a downwardly facing tapered surface 21 on the latch dog 14.

The function of the several latch elements heretofore described will beadequately explained hereinafter in connection with the description ofthe operation of the valve and latching mechanism.

The seal retainer O-ring 22 is arranged for sealing engagement betweenthe interior surface of the latch seal retainer 10 and the outer surfaceof the pressure dome 6.

The upper seal assembly 23 is retained between the lower end 24 of thelatch seal retainer 10 and an upwardly facing shoulder 25 formed aboutthe lower portion of the pressure dome 6. The upper seal assembly 23 isadapted for sealing engagement between the pressure dome 6 and thesealing bore 92 provided in the side-pocket receiver 91 of the mandrel86.

It will be understood that the novel construction and function of thevalve herein described is not limited to nor dependent upon theparticular functions and arrangement of the above described latch parts.Other latch mechanisms consistent with particular side-pocket mandrelconfigurations could be used.

The enlarged portion 26 of the pressure dome 6 has a counterbore 27arranged therein for engagement about a safety valve ring 28, saidenlarged portion 26 and the safety valve ring 28 being secured togetheras by brazing or other pressure type attachment.

There is a relatively long and cylindrical counterbore 29 in thepressure dome 6 terminating in a smaller bore 30 in which is mounted, asby threads 31a, a valve core 31 and is closed by a sealing cap 32 by themating threads 33. The valve core 31 may be of the type having a springurged check valve stem therein which may be pushed down to open thevalve for filling.

When the counterbore 29 has been charged to a predetermined pressure bya compressible fluid through valve 31 the sealing cap 32 is drawndownwardly by the mating threads 33 to compress a sealing gasket 34 toretain said predetermined pressure therein.

The safety valve ring 28 has a safety valve passage 35 therethroughadapted to receive in slidable engagement the upper portion 49 of abellows core 37. The bellows core 37 has an upwardly facing taperedsurface 38 adapted to engage the lower end of the safety bore passage 35in pressure tight relationship when the valve has stroked to its upwardlimits. There is a safety stop pin 39 secured to the upwardly extendingportion 40 of the bellows head 37 which is arranged to stop the motionof the bellows core 37 when it has stroked into its maximum position inthe downward direction.

A flexible metallic bellows 41 is brazed to the safety valve ring 28 atits lower extremity 42 and is similarly brazed to the bellows core atthe lower end as at 43.

The above described structure forms a closed and pressure tight pressurechamber which includes the dome portion 44 and bellows 41 which isfilled with a compressible fluid such as nitrogen, except for the lowerportion defined by the interior of the bellows 41, the counterbore 36,and the safety valve passage 35. The excepted areas are usually andpreferably filled with a non-compressible safety liquid 44a such assilicones in order that when conical surface 38 engages and closespassage 35 the non-compressible liquid will be trapped in the bellows 41to protect it against damage by extreme exterior pressures.

The general function of the above described pressure chamber is similarto the conventional pressure operated flow valve, except that one of theimprovements described by this invention is the dual usage of the domeportion 44 as a functional gas lift valve part and is incorporated inthe means for running, latching and retrieving the gas lift valve from aretrievable gas lift valve mandrel.

The bellows core 37 is attached by the mating threads 45 to a valve stem46. The effective length of the valve stem 46 may be adjusted by theplacement of one or more shims 47 between the valve stem and the core47.

The counterbore 48 in the lower end of the valve stem 46 has threads 49therein by which a replaceable valve stem 50 may be attached thereto.The lower end of the replaceable valve stem 50 has a valve head 51thereon, which may be made of hard material such as tungsten carbide.

The bellows housing 52 is attached to the safety valve ring 28 at themating threads 53 and depends therefrom to enclose the bellows assemblyand permanent and replaceable valve stems.

Ports 54 define a passageway for the injected gas the flow of which iscontrolled by the valve head 51. The mating threads 56 provide for rigidattachment of a latch sleeve housing 57 to the housing 52 a passageway58 therethrough and an inner upwardly facing shoulder 59 therein. Theupwardly facing shoulder 59 in the latch seal housing 57 and thedownwardly facing shoulder 55 in the bellows housing 52 retain in placea valve seat body 60. The valve seat O-ring 61 establishes a pressuretight seal between said valve seat body 60 and the latch seal housing57. A valve seat 62 is attached in the upper end of the bore 63 in thevalve seat body 60, said valve seat 62 being preferably made of tungstencarbide or similar materials.

The latch seal housing 57 has an undercut portion 64 providingdownwardly facing shoulder 65, said undercut portion and downwardlyfacing shoulder defining the position of a lower seal assembly 66. Thelower seal assembly 66 is held in place by the upper end 67 of the checkvalve seat 68, which is attached to the latch sleeve housing 57 at themating threads 69.

The lower seal assembly 66 engages the sealing bore 93 in the receptacle91 of side-pocket gas lift mandrel 86 and is in spaced relationship tothe upper seal assembly 23. Between the seal assemblies 23 and 66 thereis an enlarged bore 98 in the receptacle 91 with which ports 54 and 90communicate to provide continuous passageway for gas from the exteriorof the mandrel 86 to the interior of the flow valve.

The check valve seat 68 has an internal bore 70 therethrough which is acontinuation of the passageway 58 in the latch seal housing 57 andprovides a seating face 71 for contact with a check valve head 72 andfurther provides a counterbore 73 the function of which will behereinafter described.

The check valve head 72 has a check valve stabilizer body 74 brazed orotherwise rigidly affixed thereto, which has an internal bore 75 andports 76 through the wall defining passageways for the injected gaseither from above or below.

The check valve stabilizer 74 also has a downwardly facing shoulder 77thereabout adapted for contact with the upper end of the check valvespring 78. The lower end of the check valve spring 78 is abutted againstan upward- 1y facing shoulder 79 in the check valve housing 80. Thecheck valve housing 80 encloses the check valve ball 72 and thestabilizer 74 and is attached to the check valve seat 68 at the matingthreads 81 therebetween. The check valve housing 80 has an inwardlyextending portion 83 and a downwardly and inwardly facing contour 84thereon. The contour 84 guides the flow valve into position in thereceptacle 91 of side-pocket mandrel 86. The check valve housing 80 hasports 85 extending through the lower end thereof defining passagewaysfor the injected gas either from above or below.

The mandrel 86 has threads 87 and 88 in the upper and lower ends whichare arranged for attachment in a tubing string, the passages at each endbeing concentric with the tubing string.

The mandrel is provided with an offset portion 89 in which thereceptacle 91 is mounted. The receptacle 91 has an open lower end 94communicating with the tubing string.

A semi-circular shoulder 95 having tapered guide surfaces 96 and 97 onthe upper and lower sides thereof is provided on the inner side of theoffset portion 89 of the mandrel. The shoulder 95 is located directlyabove and concentric with the bore of the receptacle 91.

OPERATION When the flow valve representing the present invention isdesired to be run into the hole, it is attached to a running tool andkickover tool such as that described on pp. 1111 and 1112 of the 1964-65edition of the Composite Catalog of Oil Field Equipment and Services.The

flow valve is retained in the running tool by tangential shear pins (notshown) which pass through the undercut portion 4 of the latch nose 1 andbear against the downwardly facing shoulder 3 of the latch nose.Downward pressure is exerted on the flow valve by the lower end of skirtof the running tool landing against the upwardly facing shoulder 19 ofthe latch sleeve 8. The kick-over tool is manipulated as described onthe above pages of the Composite Catalog and the flow valve is deflectedlaterally into the receptacle 91 of the mandrel by the tapered profile84 of the check valve housing 80, contacting the upper end of the boreof the receptacle.

As the flow valve is inserted into the receptacle 91 the latch ring 14will contact shoulder and further movement downward of the valve willcause latch ring 14 to rise above the enlarged downward dependingportion 13 of the latch sleeve 8, simultaneously compressing the latchspring 17; but when the latch ring 14 moves adjacent the reduced portion15 of latch sleeve 8, the latch dog 14 is free to float eccentrically ofthe portion 15 and thereby be in position to move laterally sufficientto pass the shoulder 95. The downward motion of the valve is stoppedwhen the downwardly facing shoulder 10a of the latch seal retainer 10comes in contact with the upper end of the receptacle 91, and thecompressed latch spring '7 is free to force the latch dog 14 back intoposition around the enlarged downwardly depending portion 13 of thelatch sleeve 8. In this position, the latch dog 14 now being concentricwith the valve receptacle cannot move laterally to pass above theshoulder 95 and the valve will therefore be latched into the receptacle91.

The running tool and kick-over tool combination is then jarred free fromthe flow valve by shearing the tangential shear pins (not shown) inabutment with the shoulder 3 of the latch nose 1 and the tools areremoved from the hole leaving the valve in place as shown in FIGS. I andI-A.

If and when the valve is to be retrieved from the mandrel, a combinationof the kick-01f tool mentioned above and a pulling tool, generallydescribed on p. 1110 of the 1964-65 edition of the Composite Catalog OilField Equipment and Services is used. The tapered surfaces 2 of thelatch nose 1 guides the pulling tool over and around the flow valve. Thepulling tool has a collet, or latch dog arrangement which fits into theundercut 8b of the latch sleeve 8 and pulls on the flow valve throughthe shoulder 8a of the latch sleeve 8.

Inasmuch as the valve assembly is held rigidly in the receptacle 91 bymeans of the latch dog 14 in contact with the shoulder 95, upward pull,usually applied by wireline jars, will result in shearing the shearscrews 20 enabling the enlarged portion 13 of the latch sleeve 8 to bepulled upwardly from within the latch dog 14. When this occurs, thelatch dog 14 is free to fioat eccentrically within and move laterally topermit it to pass above the shoulder 95, and the combination of thekick-over tool, pulling tool and flow valve may be retrieved from thetubing.

The outside of the flow valve intermediate the upper and lower sealassemblies 23 and 66 is subjected to the annulus pressure between thecasing and tubing through ports 90. This annulus or operating pressureis communicated into the valve through the ports 54 and is effective onthe pressure reactive bellows 41 over an area determined by thedifference between the effective area of the bellows and the area of thevalve 51 co-acting with the valve seat 62. The action of the operatingpressure on the above defined areas creates a force tending to move orraise the valve 51 from the valve seat 62, and this upwardly actingforce is increased by the pressure from the tubing string communncatingthrough the ports 85, the counterbore 75, the ports 76, and around therelatively restricted passageway defined by the check valve 72 and thecounterbore 73 of the check valve seat 68 and thence upwardly throughthe passageways 70, 58 and 63 to the valve head 51 over an areadetermined by the diameter of the valve seat 62. When the sum of theabove two forces generated by the respective pressures equals thedownward force generated the gas pressure in the counterbore 29 of thepressure dome 6 (which communicates to the interior of the bellows 41through the bore 35 of the safety valve ring 28 and is thus acting onthe effective area of the bellows 41), then cracking or opening of thevalve is impending. When the valve is cracked or slightly opened, asexplained hereinabove, the annulus or operating pressure willinstantaneously become effective over the entire effective area of thebellows 41 and the valve head 51 will be further raised to completelyopen the valve. This rise of the valve head 51 is limited by contact ofthe tapered surface 38 with the safety valve ring 28 and when suchcontact is made, the non-compressible safety fluid 44a will be trappedin the bellows to protect the relatively fragile bellows from damage dueto excessive increases in pressure.

Assuming that the pressure chamber 44 has been charged with acompressible fluid to a predetermined opening pressure (pressure atwhich cracking of the valve is impending) the mechanical stroke of thebellows causes a volumetric change in the pressure chamber 44 effectiveover its effective area and will increase the charged pressure of thedome portion thereof to an extent dependent upon the volumetric capacityof the dome portion 6. This will be the maximum pressure to which thecompressible gas in the dome portion can be subjected.

It is important that the volumetric capacity of the dome portion 6 belarge enough for the pressure increase induced by the bellows stroke toresult in a maximum dome pressure substantially less than the operatingpressure of the valve. If this does not occur, the valve would reverseits stroke immediately upon a draw down in the operating pressure due togas injection into the tubing string, but conversely if there is asubstantial difference between the maximum dome pressure and theoperating pressure, injection can occur over a substantial range of thetotal pressure drop in the casing annulus before such a reversal ofstroke occurs and the valve moves toward a throttling position andeventually to a closed position.

The tubing pressure opposite a particular gas lift valve goes through awide variation during the cycle of an intermittent gas liftinstallation. At the time the valve is designed to open, there is anappreciable tubing pressure present due to the accumulation of wellfluids in the tubing above the flow valve which is subject to educationin each cycle. As explained above, when the valve is opened andinjection of annulus gas is begun, there is an immediate upsurge in thetubing pressure due to the inertia of the fluid column to be moved to adegree that approaches, if not equals, the operating pressure of thevalve. After the slug has begun movement toward the surface andinjection continues, there will be present a slowly decreasing tubingpressure with values parallel to the drawdown of the casing annuluspressure as the gas is injected under the slug.

For most eflicient operation, the installation should be designed forthe flow valve to close slightly before the slug starts emerging fromthe tubing at the surface and when this occurs, there will be a morerapid decline in the tubing pressure due to the expansion of the gaspresent and limited only by the overall operating pressure of thesystem, chiefly due to back pressure at the wellhead. Immediatelythereafter, there will be a relatively rapid increase in tubing pressuredue to the accumulation at the valve of that portion of the originalslug termed fall-back, which reaccumulates at the valve and immediatelyabove. The pressure due to fall-back (plus normal system pressure) isrepeated during each cycle. The tubing pressure opposite the valve willthen begin a relatively slow increase, which is a measure of the rateand amount of well fluids being forced into an ejectable position by thewell.

When the tubing pressure reaches a value representing the desired slug,control equipment at the well-head actuates the installation intoanother cycle by either pressure or time control.

Automatic cycling may be obtained if the tubing pressure in pasageway63, effective on the valve head 51 over the area of the valve seat 62,is the true tubing pressure, by pressure manipulation in the annulussimultaneously with the variations of the tubing pressure after thevalve is closed. This follows from the fact that although the casingpressure has been built up to the opening pressure of the valve, theopening of the valve will be prohibited by the pressure in the domeacting downwardly over the entire effective area of the bellows, andwill not 'be overcome until the tubing pressure effective on the area ofthe valve seat 62 reaches the desired point.

The above conditions could be met with a straight velocity check valvein the gas lift valve, but such a check valve would not be susceptibleto 'backflow of small degree very often present in acidizing andtreating operations. Neither would it be effective under conditions ofgas input failure wherein the slow fill-in from the well bore wouldcreate an abnormal back pressure, but at such a rate that considerableand substantial fluid could be lost into the annulus.

In contrast, the check valve assembly, described above, with the checkvalve head 72 biased into the counterbore 73 with relatively smallclearance therebetween, would be highly effective under conditions ofslow backfill and slow back pressure increases, and would be effectivelyswept into position against the check valve seat 71 to prohibit suchbackfiow. Similarly, the clearance, though small, between the checkvalve 72 and the counterbore 73 would be sufficient for communication ofthe tubing pressure and would definitely give assurance that the truetubing pressure opposite the valve is present in the passageway 63 andeffective over the area of the valve seat 62.

The true opening relationship between the above pressures is obtained asfollows: Under conditions of no flow, the check valve head 72 is urgedupwardly into the counterbore 73 of the check valve seat 68 by the checkvalve springs 78, but does not come into contact with the check valveseat 71. Furthermore, there is a relatively small clearance between thediameter of the check valve head 72 and the counterbore 73, but there isno restriction of the tubing pressure communicating through the portsand upwardly to the passageway 63 and exerting its true value on thebottom of the valve 51 over the entire area of the valve seat 62.

However, when the valve 51 is open and gas is being injected into thetubing, the velocity of flow will depress the check valve 72 bycompressing the spring 78, moving valve head 72 out of bore 73, andadequate passageway will be obtained for eflicient flow for theinjection cycle. Similarly, back-flow induced by sudden fluid surges orby the application of acidizing or treatment pressure, being restricted'by the relatively small clearance between the check valve hall and thecounterbore will sweep the check valve head 72 upwardly into engagementwith the check valve seat 71 and further flow will be effectivelyprohibited.

It may be seen then, that the proper construction of the check valveassembly will allow the calculable use of the true tubing pressurewhich, properly used in relationship to the valve seat area and theoperating pressure in the annulus, will determine an efficient valveopening limited by the structure of the bellows head 37 and the safetyvalve seat, which allows proper bellows protection against pressureoverrides, allows an optimum volume of compressible gas to 'be designedinto the valve for best and efficient use of the valve in controllingthe injection of gas from the annulus to the tubing, all of which isobtained within the structural limitations imposed by universally usedolfset mandrel equipment. This universally used mandrel equipment wasdesigned from the standpoint of efliciency in placing and removing a gaslift valve rather than from the standpoint of efliciency in the gas liftvalve itself and the valve assembly herein described adapts the valvefor most efficient use therewith.

Having described our invention we claim:

1. In a flow valve, a pressure chamber, a sealed bellows diaphragmsuspended below the pressure chamber and being in fluid communicationtherewith, said pressure chamber and bellows diaphragm being charged ata predetermined pressure; a valve stem and head suspended below thebellows diaphragm; a valve seat housing having a passage therethroughwith a valve seat thereabout arranged to receive the valve head; abellows housing about the bellows diaphragm between the pressure chamberand the seat housing; a port through the wall of the bellows housingcommunicating with the valve head and seat; and a latch assemblysurrounding the pressure chamber arranged to disengagably latch the flowvalve in a mandrel receptacle.

2. The combination called for in claim 1 with the addition of a'backflow check valve suspended below the valve seat housing having apassage therethrough communicating with passage through the valve seathousmg.

3. The combination called for in claim 2 wherein the check valveincludes a spring urged hollow body having a valve head thereon; portsthrough the wall of the hollow body below the head; the passage throughthe check valve including a counterbore with a seat at the upper endthereof, spring means urging the head toward the seat but not sufiicientto cause it to contact said seat; and an annular space between thecounterbore and the valve head.

4. In combination with a valve receiving mandrel hav- 35 therethrough, avalve head carried by the diaphragm arranged to control flow through thepassage; and means attached about the pressure chamber to latch the flowvalve in the receptacle.

5. The combination called for in claim 4 with the addition of a backflow check valve attached below the flow valve, said check valveincluding a seat, a valve head and spring means urging the valve towardthe seat but not of sufficient strength to urge the valve against theseat; there being a bore extending below the seat, the said valve beingurged into the bore by the spring means; and there being an annularpassage between the valve and the bore.

6. The combination called for in claim 4 wherein the portion of thepressure chamber With latch means thereabout extends above thereceptacle.

7. In a gas lift flow valve; a pressure chamber; a bellows diaphragmsuspended below the pressure chamber and being in communicationtherewith, a valve seat and passage therebelow; a valve head suspendedto the bellows diaphragm arranged to control flow through the passage;and latch means disposed about the pressure chamber for latching thevalve in the receptacle of a mandrel.

8. The combination called for in claim 7 with the addition of a wireline tool engaging fitting on the upper end of the valve above thelatching means.

References Cited UNITED STATES PATENTS 2,914,078 11/1959 McGowen 1371552,954,043 9/1960 Canalizo 137-155 2,959,227 11/1960 Canalizo 103232 X3,225,783 12/1965 Stacha 137-155 ALAN COHAN, Primary Examiner.

US. Cl. X.R. 103232

1. IN A FLOW VALVE, A PRESSURE CHAMBER, A SEALED BELLOWS DIAPHRAGMSUSPENDED BELOW THE PRESSURE CHAMBER AND BEING IN FLUID COMMUNICATIONTHEREWITH, SAID PRESSURE CHAMBER AND BELLOWS DIAPHRAGM BEING CHARGED ATA PREDETERMINED PRESSURE; A VALVE STEM AND HEAD SUSPENDED BELOW THEBELLOWS DIAPHRAGM; A VALVE SEAT HOUSING HAVING A PASSAGE THERETHROUGHWITH A VALVE SEAT THEREABOUT ARRANGED TO RECEIVE THE VALVE HEAD; ABELLOWS HOUSING ABOUT THE BELLOWS DIAPHRAGM BETWEEN THE PRESSURE CHAMBERAND THE SEAT HOUSING; A PORT THROUGH THE WALL OF THE BELLOWS HOUSINGCOMMUNICATING WITH THE VALVE HEAD AND SEAT; AND A LATCH ASSEMBLYSURROUNDING THE PRESSURE CHAMBER ARRANGED TO DISENGAGABLY LATCH THE FLOWVALVE IN A MANDREL RECEPTACLE.